Work twister for rolling mill

ABSTRACT

Described is apparatus adapted to be mounted on the delivery side of a rolling mill stand to receive an elongated piece of work, such as metal rod, being delivered from the mill stand and apply twisting force whereby the work enters the next stand rotated 90* as respects its passage into the preceding or delivering stand.

Unlted States Patent 51 3,699,795 Pilling [451 0a. 24, 1972 [54] WORK TWISTER FOR ROLLING MILL 1,680,105 8/ 1928 Johnson ..72/231 X Inventor: Arthur F. p n g, Torrance Weigle X [7 3] Assignee: United States Steel Corporation p Mner Mi1ton s Mehr [22] Filed: Dec 7 1970 Attorney-Donald S. Ferito [21] Appl. No.: 95,471 57 ABSTRACT Described is apparatus adapted to be mounted on the :]..C(i1 delivery Sideof a rolling mill stand to receive an elom n gated plece of work, such as metal rod, bemg Fleld of Search "72/231, delivered from the stand and twi ng ce whereby the work enters the next stand rotated 90 as [56] References Cited respects its passage into the preceding or delivering UNITED STATES PATENTS Stand- 3,330,l43 7/1967 Washburn ..72/23l X 4 Claims, 7 Drawing Figures PATENTEB 0m 24 I972 SHEET 3 OF 4 INVENTO/P ARTHUR F PILL/N6 Allomey PATENTEDUCI 24 I972 3.699.795

INVENTOR ARTHUR EP/LL/WG Alto/nay 1 WORK TWISTER FOR ROLLING MILL BACKGROUND OF TI-IEINVENTION For the purpose of simplicity, the hereinafter description of my invention refers to the work which is to be twisted or guided by the apparatus of my invention, such as metal rod, although it will be understood that the apparatus of the invention is equally adaptable to handle blooms, billets, slabs, beams, bars, channels, angles, flats, ovals, half-ovals, or any other elongated metal or other material which is operated upon by rolls.

In a rod rolling mill, it is usual practice to apply a twisting force to the rod as it leaves the delivery pass of a pair of reducing or shaping rolls in a roll stand to produce a suitable twist in the rod so that when it enters the pass of the next succeeding roll stand its cross section is aligned with that of the pass in the next succeeding roll stand. The twisting action is usually arranged to twist or turn the rod so that it will rotate approximately 90 around its longitudinal axis as it travels the distance from the delivery pass of one roll stand to the entry pass of the next succeeding roll stand.

Prior to my invention, a twist in the roll was usually effected by providing a pair of delivery stripper guides on the delivery side of the roll stand which were ground to the shape of the pass in the next succeeding mill stand, and as the rod went through the ground delivery stripper guides, a twist would be imparted thereto. A serious disadvantage inherent in this method was the fact that as the rod acquired its twist, it would be scratched by the stripper guides so that the finished product was unsuitable for prime applications.

It is, accordingly, the primary object of my invention to provide a twisting apparatus for use with rolling mills which will effectively. impart a suitable twist to the work being rolled without causing damage to the work.

It is a more specialized object of my invention to provide a twister device which is adapted to be mounted on the delivery side of a rolling mill stand and which comprises an elongated entry guide having a longitudinal passageway therethrough for the passage of work delivered from the roll stand. The receiving end of the guide is chamfered and fits closely adjacent the end of the delivery pass of the roll stand in the nip of the rolls. The opposite end of the guide is fitted in one end of a housing mounted on the rollstand. An exit guide having a passageway therethrough is rotatably mounted in the opposite end of the housing in alignment with but longitudinally spaced from the entry guide. The exit guide has an enlarged diameter portion projecting from the end of the housing remote from the entry guide which enlarged portion houses a pair of spaced twister rolls which form a pass therebetween for twisting work delivered from the entry guide. The pass between the twister rolls is at an angle to the delivery pass from which the work is received. The exit guide is adjustably rotatable within the housing so as to permit varying the angularity of the pass between the twister rolls relative to the delivery pass of the rolls in the roll stand.

These and other objects will become more apparent after referring to the following specification and attached drawings, in which:

BRIEF DESCRIPTION OF THE DRAVINGS FIG. 1 is a schematic partial plan view of a typical rolling mill utilizing the device of the invention;

FIG. 2 is an elevational view partly in section of the preferred embodiment of the invention;

FIG. 3 is an end view looking at the right end of FIG.

FIG. 4 is an exploded view in perspective of the preferred embodiment of the invention;

FIG. 5 is a side elevational view of the preferred embodiment of the invention in assembled form ready for mounting on a rolling mill stand;

FIG. 6 is a view taken substantially along the line VI-VI of FIG. 2 with parts removed for clarity; and

FIG. 7 is a side elevational view of a modified embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring more particularly to the drawing, reference numeral 2 designates generally rolling mill stands of a rolling mill each having a pair of spaced superposed reducing rolls 4 mounted therein which define a roll pass 6 therebetween. A mounting bracket 8, having a way 10 formed in the top thereof extending across the width of the rolling mill stand, is attached to the delivery side of each of the stands 2.

As shown in FIG. 1, the twister of the invention, designated generally by reference numeral 9, is mounted on the bracket 8 on the delivery side of the mill stand in each case. The twister of the invention is adapted for use, as shown in FIG. 1, with a train of rolls arranged with their axes substantially in line with each other with repeaters 13 utilized to guide the material being rolled from one roll pass to the next; and also for use with roll stands arranged in tandem with the axes of the rolls disposed substantially parallel. FIG. 1 illustrates partially a typical arrangement of roll stands in a mill for rolling rod R.

As best shown in FIG. 2, the twister of the invention includes a housing 12, formed with a dovetail projection 14 on its bottom, which is adjustably secured on the bracket 8 with the dovetail 14 slidably fitting in the way 10. The housing is secured in position by means of a gib 16 and a gib retainer plate 18.

The housing 12 is rectangular in shape having a top 20, parallel side walls 22 and 24, and a central, substantially cylindrical bore 26 extending longitudinally of the length thereof, as best shown in FIG. 2.

An entry guide 28, formed with a belled and chamfered receiving end 30 and a substantially cylindrical shank end portion 32, is disposed with the shank portion 32 rotatably fitted into the end of the housing 12 toward the roll pass 6 and the receiving end 30 fitted into the nip of the rolls at the exit end of the delivery pass 6. A central passageway 33 extends from one end to the other of the entry guide 28.

As best shown in FIGS. 2 and 4, a circumferential groove 34 is provided around the shank portion 32 intermediate its ends. A screw 36, having an unthreaded end portion 38, is threaded through a suitably tapped hole in the top 20 of the housing 12 with the unthreaded end portion 38 projecting into the groove 34. An axial hole is provided through the screw 36 with a grease fitting 39 at its upper end so as to permit the injection of grease into the groove 34. The screw 36 serves the two-fold purpose of limiting longitudinal movement of the entry guide in the housing 12 and providing access of lubricant to the shank portion 32. The receiving end of the entry guide 28 is larger in diameter than the shank portion 32 and the bore 26 so that a shoulder 41 is formed between the receiving end 30 and the shank portion 32 which shoulder abuts against the outer end of the housing 12 and thereby limits the depth of penetration of the entry guide into the housing bore.

An exit guide is formed with a substantially cylindrical shank portion 42 and an enlarged bifurcated end 44 integral with the shank portion 42. A substantially central passageway 45 extends from one end of the exit guide 40 to its other end and communicates with the space between the tines of the bifurcated end 44. The passageway 45 is belled at its inner end 47 so as to facilitate reception of a rod from the entry guide 28.

The exit guide 40 is disposed with its shank portion 42 rotatably fitted in the end of the bore 26 of the housing 12 in alignment with but spaced from the shank portion 32 of the entry guide 28. Similar to the shank portion 32 of the entry guide 28, the shank portion 42 of the exit guide 40 is provided with a circumferential groove 46 therearound intermediate its ends. A screw 48, similar to screw36, is threaded through the top of the housing into the groove 46 to limit the longitudinal movement of the shank 42 in the bore 26 and also to provide means for introducing lubrication to the shank 42. A grease fitting 49 is provided on the screw 48. The bifurcated end 44 of the exit guide 40 has a cross-sectional area greater than the cross-sectional area of the bore 26 and the shank portion 42.

A ring gear 50 is disposed circumferentially around the shank portion 42 outside of the housing 12 fixedly attached to the rearward side 51 of the bifurcated end portion 44. A bifurcated plate 52 is rigidly mounted across the top 20 of the housing 12 adjacent the end thereof remote from the mill stand. A worm gear 54 is carried by the plate 52 and meshes with the ring gear 50 to adjustably rotate the exit guide about its longitudinal axis to impart the desired amount of twist to the rod as it leaves the exit guide 40.

A pair of twister rolls 56 having internal bearings are mounted on fixed shafts 58 received in holes 60 through the tines 62 of the bifurcated end portion 44. The holes 60 are equally spaced as respects the center of the passageway 45. The center-to-center distance of the holes 60 is fixed in relation to the diameter of the rolls 56 to create a roll-gap 64 of desired dimension between the roll 60 which is greater than the minor but less than the major cross-section dimension of the rod R to be delivered from the rolling mill stand 2. For a given center-to-center spacing between the holes 60 in each of the side walls 62, the roll-gap 64 can be varied to accommodate a range of rod sizes by providing rolls of varying diameters. The shafts 58 are held in position by a lock-bar 66 secured by a cap screw 68 to one of the tines 62. This arrangement facilitates changing of the twister rolls 56 as required by changes in thesize of rod being rolled. The shafts 58 of the rolls 56 are drilled and tapped to receive grease fittings 70 at the ends thereof opposite the lock-bar 66.

The front faces 72 of the tines 62 are provided with tapped holes to receive cap screws 74 for mounting an exit tube 76 which communicates with the gap 64 and projects from the forward end of the bifurcated portion 44 for the obvious purpose of guiding a rod therefrom.

As best shown in FIG. 2, the combined length of the shank portions 32 and 44 is less than the total length of the bore 26 of the housing l2 and, as described herein before, the entry guide and exit guide are inserted into the bore 26 to the limit established by the shoulder 41 and the enlarged bifurcated portion 44 with the ring gear 5%) attached thereto. This arrangement creates an internal groove 78 in the bore 26 intermediate its ends. A tapped hole or port 80 through the top portion 20 of the housing 12, as best shown in FIGS. 2 and 6, is centered with respect to the groove 78 and drilled tangentially to the bore 26. A fixture 82 is connected with the port 80 to introduce cooling fluid under pressure thereto. The tangential arrangement of the port 80 relative to the bore 26 and the groove 78 permits cooling water or other fluid introduced into the bore 26 through the port 80 to swirl forcefully in the groove 78 and flush out any detached scale; the water and scale being discharged through the passageways 33 and 45.

As best shown in FIGS. 4, 5 and 6, the side 22 of the housing 12 is slit longitudinally as at 86 from one end to the other and the opposite side wall 24 is formed with a blind slot 88 extending longitudinally from one end to the other of the housing 12. The blind slot opens to the outer surface of the wall 24, as best shown in FIGS. 4 and 6. The slit 86 and the blind slot 88 are substantially parallel and extend along a horizontal plane through the center 'line of the bore 26. A pair of spaced blind holes 90 are drilled from the top of the side wall 22 to extend a substantial distance below the slit 86. Clamp screws 92 are fitted into the holes 90 and are threaded into the tapped blind portions thereof below the slit 86. This arrangement affords a clamping arrangement for aiding in holding the entry guide and exit guide in desired positions.

In operation, the exit guide 40 is rotated by turning the worm gear 54 so that the birfurcated portion is positioned with the parallel tines 22 and 24 thereof displaced 15 to 45 from the vertical. The amount of rotation required varies with the shape rod or other material being rolled, the distance between the rolling mill stands and other factors of mill design; and is determined by trial. The optimum degree of rotation is that which will apply just sufficient twist to the rod to cause it to be rotated 90 by the time it enters the next stand. The interrneshing of the worm gear 54 and the ring gear 50 together with the action of the lock screw 92 adjacent to the bifurcated portion 44 will act to maintain the exit guide 40 in the adjusted position.

FIG. 7 illustrates a modified embodiment of the twister of the invention wherein elements similar to elements of the preferred embodiment are designated by the same reference numerals but primed. In this embodiment there is no ring gear or worm gear. Adjustments are made by hand by grasping the bifurcated portion 44' of the exit guide 40' and rotating it to the desired position. The lock screw 92' adjacent the bifurcated portion 44' clamps the housing so that the exit guide is held or maintained in the desired position. The modified embodiment of the invention with its simpler design can be used where fine adjustments, possible with the ring gear and worm gear of the main embodiment, are not necessary.

While I have shown but two embodiments of my in vention, other adaptations and modifications may be made without departing from the scope of the following claims.

I claim:

1. In a rolling mill including a plurality of rolling mill stands each housing a pair of rolls therein, each of said pairs of rolls formed with at least one pass therebetween for the passage of elongated work being rolled, the improvement therewith of a twister device mounted on the side of at least one of said roll stands, said device comprising an elongated first guide having a longitudinal passageway therethrough for the passage of work passing between a pair of said roll stands, one end of said guide being chamfered and fitting closely adjacent the end of a pass in one of said pair of 'roll stands, the opposite end of said guide fitting in one end of a housing mounted on said at least one of said roll stands, a second guide having a longitudinal passageway therethrough rotatably mounted in the opposite end of said housing aligned with but longitudinally spaced from said first guide, said housing having a longitudinal bore therethrough for receiving said guides, a top and bottom and opposed lateral side walls, said first guide including a shank portion adjacent its said one end adapted to fit slidingly in said housing, the outer diameter of said one end of said first guide being greater than the outer diameter of said shank and greater than the diameter of the bore of said housing thereby forming a shoulder on said first guide, said shoulder normally abutting the end of said housing thereby limiting the depth of penetration of said first guide into said housing, said shank having a circumferential slot therearound intermediate the ends thereof, a locking screw projecting through the top of said housing into said slot to lock said shank against longitudinal movement in said housing, one end of said second guide projecting from the end of said housing remote from said first guide, a pair of spaced twister rolls in the said one end of said second guide forming a pass therebetween for twisting work received by said second guide, the pass between said twister rolls being at an angle to the pass between the rolls in said at least one of said roll stands, said second guide being adjustably rotatable in said housing to vary the angularity of the pass between said twister rolls relative to the pass between the rolls in said at least one of said roll stands.

2. In a rolling mill including a plurality of rolling mill stands each housing a pair of rolls therein, each of said pairs of rolls formed with at least one pass therebetween for the passage of elongated work being rolled, the improvement therewith of a twister device mounted on the side of at least one of said roll stands, said device comprising an elongated first guide having a longitudinal passageway therethrough for the passage of work passing between a pair of said roll stands, one end of said guide being chamfered and fitting closely adjacent the end of a pass in one of said pair of roll stands, the opposite end of said guide fitting in one end of a housing mounted on said at least one of said roll stands, a second guide having a longitudinal passageway therethrough rotatably mounted in the opposite end of said housing aligned with but longitudinally spaced from said first guide, said housing having a longitudinal bore therethrough for receiving said guides, a top and bottom and opposed lateral side walls, said second guide including a shank portion fitting in the end of said housing bore remote from said first guide and an enlarged portion projecting from said lastnamed end of said housing bore, said enlarged portion being bifurcated, said last-named shank portion having a circumferential slot therearound intermediate its ends, a locking screw projecting through the top of said housing into said last-named slot to lock said second guide against longitudinal movement in said housing, a pair of spaced twister rolls in said bifurcated end of said second guide forming a pass therebetween for twisting work received by said second guide, the pass between said twister rolls being at an angle to the pass between the rolls in said at least one of said roll stands, said second guide being adjustably rotatable in said housing to vary the angularity of the pass between said twister rolls relative to the pass between the rolls in said at least one of said roll stands.

3. In a rolling mill including a plurality of rolling mill stands each housing a pair of rolls therein, each of said pairs of rolls formed with at least one pass therebetween for the passage of elongated work being rolled, the improvement therewith of a twister device mounted on the side of at least one of said roll stands, said device comprising an elongated first guide having a longitudinal passageway therethrough for the passage of work passing between a pair of said roll stands, one end of said guide being chamfered and fitting closely adjacent the end of a pass in one of said pair of roll stands, the opposite end of said guide fitting in one end of a housing mounted on said at least one of said roll stands, a second guide having a longitudinal passageway therethrough rotatably mounted in the opposite end of said housing aligned with but longitudinally spaced from said first guide, said housing having a longitudinal bore therethrough for receiving said guides, a top and bottom and opposed lateral side walls, said first and second guides each having a shank portion fitting into opposite ends of said housing, said housing being substantially rectangular in shape having a slit extending longitudinally thereof along one lateral side and a blind slot extending longitudinally along the opposite lateral side thereof, said slot being open to the outer surface of said housing, at least one clamp screw threaded into the slit side of said housing normal to said slit to a depth below said slit adapted to diminish and expand the diamter of the bore of said housing relative to the outer circumferences of the shank portions of said first and second guides, one end of said second guide projecting from the end of said housing remote from said first guide, a pair of spaced twister rolls in said one end of said second guide forming a pass therebetween for twisting work received by said second guide, the pass between said twister rolls being at an angle to the pass between the rolls in said at least one of said roll stands, said second guide being adjustably rotatable in said housing to vary the angularity of the pass between said twister rolls relative to the pass between the rolls in said at least one of said roll stands.

4. In a rolling mill including a plurality of rolling mill stands each housing a pair of rolls therein, each of said pairs of rolls formed with at least one pass therebetween for the passage of elongated work being rolled, the improvement therewith of a twister device mounted on the side of at least one of said roll stands, said device comprising an elongated first guide having a longitudinal passageway therethrough for the passage of work passing between a pair of said roll stands, one end of said guide being chamfered and fitting closely adjacent the end of a pass in one of said pair of roll stands, the opposite end of said guide fitting in one end of a housing mounted on said at least one of said roll stands, a second guide having a longitudinal passageway therethrough rotatably mounted in the opposite end of said housing aligned with but longitudinally spaced from said first guide, said housing having a longitudinal bore therethrough for receiving said guides, a top and bottom and opposed lateral side walls, one end of said second guide projecting from the end of said housing remote from said first guide, a pair of spaced twister rolls in said one end of said second guide forming a pass therebetween for twisting work received by said second guide, the pass between the rolls in said at least one of said roll stands, said second guide being adjustably rotatable in said housing to vary the angularity of the pass between said twister rolls relative to the pass between the rolls in said at least one of said roll stands, and rotating means on said housing connected with said exit guide for rotating said second guide to vary the angularity of the pass between said twister rolls relative to the pass between the rolls in said at least one of said roll stands, said rotating means comprising a ring gear rigidly mounted circumferentially on said second guide adjacent the end of said housing remote from said first guide, and a worm gear rotatabiy mounted on said housing in mesh with said ring gear. 

1. In a rolling mill including a plurality of rolling mill stands each housing a pair of rolls therein, each of said pairs of rolls formed with at least one pass therebetween for the passage of elongated work being rolled, the improvement therewith of a twister device mounted on the side of at least one of said roll stands, said device comprising an elongated first guide having a longitudinal passageway therethrough for the passage of work passing between a pair of said roll stands, one end of said guide being chamfered and fitting closely adjacent the end of a pass in one of said pair of roll stands, the opposite end of said guide fitting in one end of a housing mounted on said at least one of said roll stands, a second guide having a longitudinal passageway therethrough rotatably mounted in the opposite end of said housing aligned with but longitudinally spaced from said first guide, said housing having a longitudinal bore therethrough for receiving said guides, a top and bottom and opposed lateral side walls, said first guide including a shank portion adjacent its said one end adapted to fit slidingly in said housing, the outer diameter of said one end of said first guide being greater than the outer diameter of said shank and greater than the diameter of the bore of said housing thereby forming a shoulder on said first guide, said shoulder normally abutting the end of said housing thereby limiting the depth of penetration of said first guide into sAid housing, said shank having a circumferential slot therearound intermediate the ends thereof, a locking screw projecting through the top of said housing into said slot to lock said shank against longitudinal movement in said housing, one end of said second guide projecting from the end of said housing remote from said first guide, a pair of spaced twister rolls in the said one end of said second guide forming a pass therebetween for twisting work received by said second guide, the pass between said twister rolls being at an angle to the pass between the rolls in said at least one of said roll stands, said second guide being adjustably rotatable in said housing to vary the angularity of the pass between said twister rolls relative to the pass between the rolls in said at least one of said roll stands.
 2. In a rolling mill including a plurality of rolling mill stands each housing a pair of rolls therein, each of said pairs of rolls formed with at least one pass therebetween for the passage of elongated work being rolled, the improvement therewith of a twister device mounted on the side of at least one of said roll stands, said device comprising an elongated first guide having a longitudinal passageway therethrough for the passage of work passing between a pair of said roll stands, one end of said guide being chamfered and fitting closely adjacent the end of a pass in one of said pair of roll stands, the opposite end of said guide fitting in one end of a housing mounted on said at least one of said roll stands, a second guide having a longitudinal passageway therethrough rotatably mounted in the opposite end of said housing aligned with but longitudinally spaced from said first guide, said housing having a longitudinal bore therethrough for receiving said guides, a top and bottom and opposed lateral side walls, said second guide including a shank portion fitting in the end of said housing bore remote from said first guide and an enlarged portion projecting from said last-named end of said housing bore, said enlarged portion being bifurcated, said last-named shank portion having a circumferential slot therearound intermediate its ends, a locking screw projecting through the top of said housing into said last-named slot to lock said second guide against longitudinal movement in said housing, a pair of spaced twister rolls in said bifurcated end of said second guide forming a pass therebetween for twisting work received by said second guide, the pass between said twister rolls being at an angle to the pass between the rolls in said at least one of said roll stands, said second guide being adjustably rotatable in said housing to vary the angularity of the pass between said twister rolls relative to the pass between the rolls in said at least one of said roll stands.
 3. In a rolling mill including a plurality of rolling mill stands each housing a pair of rolls therein, each of said pairs of rolls formed with at least one pass therebetween for the passage of elongated work being rolled, the improvement therewith of a twister device mounted on the side of at least one of said roll stands, said device comprising an elongated first guide having a longitudinal passageway therethrough for the passage of work passing between a pair of said roll stands, one end of said guide being chamfered and fitting closely adjacent the end of a pass in one of said pair of roll stands, the opposite end of said guide fitting in one end of a housing mounted on said at least one of said roll stands, a second guide having a longitudinal passageway therethrough rotatably mounted in the opposite end of said housing aligned with but longitudinally spaced from said first guide, said housing having a longitudinal bore therethrough for receiving said guides, a top and bottom and opposed lateral side walls, said first and second guides each having a shank portion fitting into opposite ends of said housing, said housing being substantially rectangular in shape having a slit extending longitudinally thereof along oNe lateral side and a blind slot extending longitudinally along the opposite lateral side thereof, said slot being open to the outer surface of said housing, at least one clamp screw threaded into the slit side of said housing normal to said slit to a depth below said slit adapted to diminish and expand the diamter of the bore of said housing relative to the outer circumferences of the shank portions of said first and second guides, one end of said second guide projecting from the end of said housing remote from said first guide, a pair of spaced twister rolls in said one end of said second guide forming a pass therebetween for twisting work received by said second guide, the pass between said twister rolls being at an angle to the pass between the rolls in said at least one of said roll stands, said second guide being adjustably rotatable in said housing to vary the angularity of the pass between said twister rolls relative to the pass between the rolls in said at least one of said roll stands.
 4. In a rolling mill including a plurality of rolling mill stands each housing a pair of rolls therein, each of said pairs of rolls formed with at least one pass therebetween for the passage of elongated work being rolled, the improvement therewith of a twister device mounted on the side of at least one of said roll stands, said device comprising an elongated first guide having a longitudinal passageway therethrough for the passage of work passing between a pair of said roll stands, one end of said guide being chamfered and fitting closely adjacent the end of a pass in one of said pair of roll stands, the opposite end of said guide fitting in one end of a housing mounted on said at least one of said roll stands, a second guide having a longitudinal passageway therethrough rotatably mounted in the opposite end of said housing aligned with but longitudinally spaced from said first guide, said housing having a longitudinal bore therethrough for receiving said guides, a top and bottom and opposed lateral side walls, one end of said second guide projecting from the end of said housing remote from said first guide, a pair of spaced twister rolls in said one end of said second guide forming a pass therebetween for twisting work received by said second guide, the pass between the rolls in said at least one of said roll stands, said second guide being adjustably rotatable in said housing to vary the angularity of the pass between said twister rolls relative to the pass between the rolls in said at least one of said roll stands, and rotating means on said housing connected with said exit guide for rotating said second guide to vary the angularity of the pass between said twister rolls relative to the pass between the rolls in said at least one of said roll stands, said rotating means comprising a ring gear rigidly mounted circumferentially on said second guide adjacent the end of said housing remote from said first guide, and a worm gear rotatably mounted on said housing in mesh with said ring gear. 